Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1 | // run |
| 2 | |
| 3 | // Copyright 2016 The Go Authors. All rights reserved. |
| 4 | // Use of this source code is governed by a BSD-style |
| 5 | // license that can be found in the LICENSE file. |
| 6 | |
| 7 | package main |
| 8 | |
| 9 | import ( |
| 10 | "fmt" |
| 11 | "runtime" |
| 12 | ) |
| 13 | |
| 14 | var sink *[20]byte |
| 15 | |
| 16 | func f() (x [20]byte) { |
| 17 | // Initialize x. |
| 18 | for i := range x { |
| 19 | x[i] = byte(i) |
| 20 | } |
| 21 | |
| 22 | // Force x to be allocated on the heap. |
| 23 | sink = &x |
| 24 | sink = nil |
| 25 | |
| 26 | // Go to deferreturn after the panic below. |
| 27 | defer func() { |
| 28 | recover() |
| 29 | }() |
| 30 | |
| 31 | // This call collects the heap-allocated version of x (oops!) |
| 32 | runtime.GC() |
| 33 | |
| 34 | // Allocate that same object again and clobber it. |
| 35 | y := new([20]byte) |
| 36 | for i := 0; i < 20; i++ { |
| 37 | y[i] = 99 |
| 38 | } |
| 39 | // Make sure y is heap allocated. |
| 40 | sink = y |
| 41 | |
| 42 | panic(nil) |
| 43 | |
| 44 | // After the recover we reach the deferreturn, which |
| 45 | // copies the heap version of x back to the stack. |
| 46 | // It gets the pointer to x from a stack slot that was |
| 47 | // not marked as live during the call to runtime.GC(). |
| 48 | } |
| 49 | |
| 50 | var sinkint int |
| 51 | |
| 52 | func g(p *int) (x [20]byte) { |
| 53 | // Initialize x. |
| 54 | for i := range x { |
| 55 | x[i] = byte(i) |
| 56 | } |
| 57 | |
| 58 | // Force x to be allocated on the heap. |
| 59 | sink = &x |
| 60 | sink = nil |
| 61 | |
| 62 | // Go to deferreturn after the panic below. |
| 63 | defer func() { |
| 64 | recover() |
| 65 | }() |
| 66 | |
| 67 | // This call collects the heap-allocated version of x (oops!) |
| 68 | runtime.GC() |
| 69 | |
| 70 | // Allocate that same object again and clobber it. |
| 71 | y := new([20]byte) |
| 72 | for i := 0; i < 20; i++ { |
| 73 | y[i] = 99 |
| 74 | } |
| 75 | // Make sure y is heap allocated. |
| 76 | sink = y |
| 77 | |
| 78 | // panic with a non-call (with no fallthrough) |
| 79 | for { |
| 80 | sinkint = *p |
| 81 | } |
| 82 | |
| 83 | // After the recover we reach the deferreturn, which |
| 84 | // copies the heap version of x back to the stack. |
| 85 | // It gets the pointer to x from a stack slot that was |
| 86 | // not marked as live during the call to runtime.GC(). |
| 87 | } |
| 88 | |
| 89 | func main() { |
| 90 | x := f() |
| 91 | for i, v := range x { |
| 92 | if v != byte(i) { |
| 93 | fmt.Printf("%v\n", x) |
| 94 | panic("bad f") |
| 95 | } |
| 96 | } |
| 97 | x = g(nil) |
| 98 | for i, v := range x { |
| 99 | if v != byte(i) { |
| 100 | fmt.Printf("%v\n", x) |
| 101 | panic("bad g") |
| 102 | } |
| 103 | } |
| 104 | } |